Chp' 33 EM oscillations

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• Chapter 33
• Electromagnetic oscillations Alternating
  Current

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33-6 Alternating Currents
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33-8 Three Simple Circuits
Resistive circuit
     

Current (I) and voltage (V) have the same time
dependence.

? IN PHASE
Capacitive circuit
I and V out of phase, V follows I by 90o
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Inductive circuit
I and V out of phase, I follows V by 90o
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Solved example A 500 mH inductor is connected in
series with a 10 V AC power supply. Determine
the inductive reactance of the inductor and the
current through it if the frequency of the source
voltage is 50 Hz. Determine this if the
frequency is 10 kHz. As the
frequency? the resistance to change (inductive
reactance) increases.
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• Oscillations in circuits (LC) (33  2)
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• Current and voltage oscillate

 

• Assume circuit resistance is zero (R  0).
• Exhibits oscillatory behavior ? mass on a spring
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• Current and voltage will oscillate.
•     Capacitor is fully charged The total energy
  is stored in the capacitor (UE  q2/2C) and
  current is zero.
• As capacitor begins to discharge, current flow
  increases and some energy is stored in the
  magnetic field of the inductor.

Therefore energy is transferred from the
electric field (capacitor to the magnetic field
of the inductor).   

• When the capacitor is fully discharged, it
  stores no energy and all the energy is stored in
  the inductor.

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Derivation of oscillation frequency of an LC
circuit (undamped oscillation)
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33-5 Damped Oscillations in circuits (RLC)
  Derivation of oscillation
frequency of a RLC circuit (damped
oscillation)
? determines the rate of exponential damping of
charge and current in a circuit containing an
inductor, capacitor and resistor. The degree of
damping depends on R and L.
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